Femoral component of an artificial knee joint

The following patent application is being filed in coordination with another patent application having a very similar disclosure and related to other portions of a common artificial knee joint. This other corresponding application is entitled “TIBIAL COMPONENT OF AN ARTIFICIAL KNEE JOINT,” has the same inventor, was filed on the same day and has Docket No. 07112.101.

The following invention relates to surgical implants placed within a knee of a patient to function as an artificial knee joint. More particularly, this invention relates to artificial knee joints which include a femoral component, a tibial component and a patellar component which exhibit a simplified femoral component, femoral component sizing, bone preparation procedures, tibial component meniscal insert low wear characteristics and dual direction knee pivoting rotation function therein.

Human knee joints endure exceptional loads and a wide variety of loading scenarios throughout the life of an individual. While the human knee joint is capable of supporting most of these typical loads under normal conditions for the life of the individual, in certain circumstances the human knee joint suffers degraded performance. For instance, injury can occur to the knee causing the knee to not fully repair itself, or not being fully repairable through medical intervention, such that it becomes beneficial to replace the knee joint with an artificial knee joint. In other circumstances, degenerative disease can act on the natural knee joint to degrade its performance in an irreversible fashion, such that replacement of the natural knee joint with an artificial knee joint is indicated.

Artificial knee joints are well known in the literature and have come into widespread use. In general, such artificial knee joints include a femoral component, a tibial component and a patellar component. The distal end of the femur is surgically prepared to have the distal end thereof have a contour matching an internal box surface of the femoral component. The femoral component is then attached to the distal end of the femur. Similarly, the proximal end of the tibia is prepared, typically by cutting a flat proximal surface on the proximal end of the tibia, and the tibial component is attached to this proximal end of the tibia. Muscles and ligaments surrounding the knee are disturbed as little as possible so that they can continue to function in the same manner that they do with a natural knee joint. Proximal surfaces of the tibial component and distal surfaces of the femoral component abut each other and are designed to facilitate articulation relative to each other in the same way that the distal end of a natural femur articulates relative to the proximal end of a natural tibia. Typically, an insert of materials somewhat more flexible and resilient than metal is attached to a proximal end of the tibial component, with other portions of the tibial component formed of a more rigid material, such as titanium or cobalt chrome. This insert in some ways duplicates the function of a natural meniscus within a natural knee joint, and helps to minimize friction in the articulation of the femoral component relative to the tibial component. Numerous drawbacks have been noted with prior art artificial knee joints and for which this invention strives to provide a significant and beneficial improvement. For instance, artificial knee joints are known for being somewhat complex to implant, and most particularly the femoral component. In particular, the distal end of the femur must be extensively shaped to properly mate with facets on the internal box face of the femoral component.

In the prior art, the surgeon must make numerous very precise cuts on the distal end of the femur and these cuts vary based on the particular geometry of the facets on the internal box face of the femoral component. Because different human bodies have different sizes, various different femoral components having different sizes must be considered before selecting the particular femoral component. Typically, a cutting jig or other specialized tool must be selected that matches with the femoral component selected so that the cuts are properly made.

As a result, the surgeon, manufacturer or an associated health care facility must maintain an extensive inventory of femoral cutting jigs for potential use in an artificial knee joint surgical procedure. Such extensive inventory of cutting jigs is expensive to maintain, requires additional space within the surgery room or nearby, and presents the greater possibility of problems during or after surgery. Furthermore, an increase of such cutting jigs is more difficult to clean and sterilize which increases the potential for infection, in turn resulting in a less than fully desirable outcome. U.S. Pat. Nos. 5,925,049 and 5,749,876 both describe a femoral cutting instrument sizer that allows a single tool to be used for a set of femoral components of different sizes however both devices are cumbersome and complicated to use. Accordingly, a need exists for an artificial knee joint which has a femoral component which is one of a set of femoral components of different sizes which share as many shape and size characteristics as possible, as well as a single tool which can easily make the necessary cuts for all different femoral component sizes.

Another problem with known prior art artificial knee joints is that they cannot duplicate the large amount of flexion produced by a natural human knee joint and still provide sufficient contact between the artificial femur and the tibial component. Conventional artificial knee joints are limited in further flexion because they typically cause the femur or structure coupled to the femur to abut the tibia or structures coupled to the tibia to prevent further flexion. Accordingly, a need exists for an artificial knee joint which can provide as much flexion as possible to more fully mimic a natural knee joint in performance.

Another problem with known prior art artificial knee joints is their inability or difficulty in facilitating knee pivoting rotation in both clockwise and counterclockwise directions. A natural knee joint is capable of a small amount of pivoting rotation. Such pivoting rotation is particularly desirable when a person is walking along a curving path. Some artificial knee joints, such as those taught by Hodge (U.S. Pat. No. 5,413,604) allow for pivoting rotation of the medial condyle about the lateral condyle, but not rotation of the lateral condyle. Furthermore, other artificial knee joints, such as those taught by Kaufman (U.S. Pat. No. 6,013,103) and Tuke (U.S. Pat. No. 5,219,362) describe pivoting rotation of the lateral condyle about the medial condyle. Accordingly, a need exists for complete replication of function of a natural knee joint, including pivoting rotation in both directions.

Another problem with known prior art artificial knee joints is the need for the insert or other meniscal structure to exhibit a minimum thickness for suitable wear characteristics and duration, while minimizing an amount of bone required to be removed from the proximal end of the tibia. Generally speaking, bone is removed from the proximal end of the natural tibia in an amount equaling a height of portions of the tibial component of the artificial knee joint which extend beyond the proximal surface of the tibia after it has been prepared for receiving the tibial component. Typically, regulatory authorities recommend a six millimeter thickness on the insert or other meniscal wear structure, and structural portions of the tibial component need approximately four millimeters for sufficient strength, a full ten millimeters of bone must be removed from the proximal tibia to maintain proper ligament tension and maintain patient leg length. It is desirable to remove as little natural bone as possible, as natural bone is beneficial in many respects and to be preferred over artificial structures to the extent possible.

Prior art attempts have been made to nest the insert into the tibial component somewhat, but only with joints that prevent twisting. See for instance patent to Aubriot (U.S. Pat. No. 5,326,358) and Johnson (U.S. Pat. No. 4,568,348). Accordingly, a need exists for a tibial component of an artificial knee joint which can maintain the regulatory recommended thickness of an insert or other wear structure while minimizing a height of other portions of the tibial component of the artificial knee joint, and still allow twisting, to minimize the amount of required bone removal from the proximal end of the tibia.

With this invention, an artificial knee joint is provided which includes a femoral component and a tibial component that together satisfy the needs and shortcomings of the prior art identified above. The joint includes a femoral component surgically affixable to a distal end of a femur and a tibial component surgically affixable to a proximal end of a tibia. An insert is also provided as a portion of the tibial component which is removably attachable to the tibial component.

With this invention a jig is also provided to assist in making the cuts necessary to form surfaces on the distal end of the femur appropriate to mate with facets on an internal box face of the femoral component. This jig includes slots or other guides for a cutting tool so that the jig helps the surgeon who is wielding the cutting tool to cut the proper portions of the distal end of the femur away to provide the required surfaces on the distal end of the femur.

The jig is provided to make appropriate cuts for multiple different sizes of femoral components. In particular, slots or other cutting tool guide structures are provided which are the same for each size femoral component to be surgically implanted, except for an anterior surface cut which is made at a variable distance from a posterior surface cut, depending on a size of the femoral component to be implanted. Other slots or other structures within the jig are the same for other cuts to be made to form the surfaces on the distal end of the femur for proper fit with the selected femoral component. Adjustability of the jig for cutting of the anterior surface is in one embodiment provided by a plurality of separate anterior slots within the jig. In another embodiment, the jig is provided with an anterior slot on a moving portion of the jig that can slide relative to fixed portions of the jig to a desired position for making the necessary cut to form the anterior surface on the distal end of the femur.

The femoral component is generally in the form of a surfacing structure providing a new wear surface on the distal end of the femur. As such it includes a patellar flange portion adapted to be placed adjacent the anterior surface of the distal end of the femur and a medial condylar leg and a lateral condylar leg, both extending down from the patellar flange portion generally parallel to each other. The condylar legs curve posteriorly as they extend from the patellar flange portion.

A distal and posterior face of the femoral component is provided primarily upon the medial condylar leg and lateral condylar leg and is adapted to abut with the insert of the tibial component of the artificial knee joint. The internal box face of the femoral component includes an anterior facet, a distal facet, a posterior facet, and preferably a pair of diagonal facets at either side of the distal facet. The posterior facet is angled back toward a centerline of the femoral component as the posterior facet extends away from the distal facet. Such a negative angle for the posterior facet of the internal box surface and corresponding forming of the posterior surface on the distal end of the femur, allows the distal face of the two condylar legs to wrap around the posterior side of the distal end of the femur sufficiently farther to allow an increase of contact and flexion in operation of the knee joint when compared to prior art knee joint femoral components.

The tibial component includes a substantially planar plate oriented substantially perpendicular to a shaft which is adapted to pass down into a marrow of the tibia and substantially coaxial with a centerline of the tibia. The insert is supported upon a proximal side of the plate. A dovetail rib extends in an anterior to posterior direction from the proximal surface of the plate. The insert includes a dovetail recess sized to be aligned with the dovetail rib on the plate so that the insert can be slid onto the dovetail rib and held tightly to the proximal surface of the plate.

To minimize a thickness of the plate and an overall height of the combination of the insert and the plate, the proximal surface of the plate includes depressions therein and a distal surface of the insert includes lobes therein that drop down into the depressions in the proximal surface of the plate. In this way, a maximum thickness of the insert is maintained, especially beneath wells in a proximal surface of the insert, without adding height to the overall insert and plate of the tibial component.

Two wells in the proximal surface of the insert have a curvature matching a curvature of the condylar legs of the femoral component. Thus, the condylar legs of the femoral component can reside within these generally spherical wells in the insert and the joint can experience flexion while maintaining surface contact between the wells of the insert and the condylar legs of the femoral component.

The wells have valleys that extend arcuately and mostly in an anterior direction away from low points of the wells. These valleys are of lesser depth in a distal direction as the valleys extend anteriorly away from low points of the wells. The valleys curve about a center point axis aligned with the low point of the other of the pair of wells. Side walls of the valleys are appropriately gradual so that cross-sections of the valleys perpendicular to centerlines of the valleys contain a curvature similar to that of the condylar legs of the femoral component. In this way, one of the condylar legs can remain at a low point within one of the wells while the other condylar leg can rotate along a valley of one of the wells away from the low point and moving slightly upwardly in a proximal direction. As the elevation of the valleys increase, tension on ligaments and muscles of the knee joint tighten to resist further pivoting rotation of the knee joint. Gravity loads tend to encourage the condylar legs back to the low points of the wells, as well as forces applied by the ligaments and muscles themselves. Such pivoting rotation can occur in either direction with one of the condylar legs remaining in a low point of one of the wells while the other condylar leg can move arcuately within its well. In this way, a small amount of knee pivoting rotation action is provided by the artificial knee joint of this invention, mimicking performance of a natural knee joint being replaced.